Wolff-Parkinson-White Syndrome

In the left illustration, the arrows represent electrical signals beginning at the sinus node or "spark plug" in the heart, activating both atria and then passing through the atrioventricular (AV) node, or "relay station," on the way to the ventricles. The panel below the heart is a typical electrocardiogram (ECG or EKG) recording of a normal heart rhythm

Wolff-Parkinson-White syndrome — In the right illustration of the heart, the arrows represent the path of electrical activity. The accessory pathway is an abnormal "bridge" of tissue that allows the heart's electrical impulse to travel in a circular pattern from the ventricles to the atria. The panels below the heart are typical electrocardiogram recordings from a heart with WPW with an accessory pathway (left) and a heart with tachycardia (right).